Perennial herbs, with corms, bulbs or tuberous roots, sheathing entire leaves, sometimes reduced to scales, the flowers perfect, irregular, bracted, solitary, spiked or racemed.
Perianth superior, of 6 segments, the 3 outer (sepals) similar or nearly so, 2 of the inner ones (petals) lateral, alike;
the third inner one (lip) dissimilar, often markedly so, usually larger, often spurred, sometimes inferior by torsion of the ovary or pedicel.
Stamens variously united with the style into an unsymmetrical column;
anther 1, or in a few genera 2, 2-celled;
pollen in 2-8 pear-shaped usually stalked masses (pollinia), united by elastic threads, the masses waxy or powdery, attached at the base to a viscid disk (gland).
Style often terminating in a beak (rostellum) at the base of the anther or between its sacs.
Stigma a viscid surface, facing the lip beneath the rostellum, or in a cavity between the anther-sacs (clinanclrium).
Ovary inferior, usually long and twisted, 3-angled, 1-celled;
ovules numerous, anatropous, on 3 parietal placentae.
Capsule 3-valved.
Seeds very numerous, minute, mostly spindle-shaped, the loose coat hyaline, reticulated;
endosperm none;
embryo fleshy.

About 430 genera and over 5000 species, of wide distribution, most abundant in the tropics, many of those of warm regions epiphytes.